Apple’s ECG app that will permit Series 4 watch wearers to take an electrocardiograph reading on the go will release publicly as part of the watchOS 5.1.2 software update.

MacRumors learned about this from an internal Apple Store training document.

The ECG app is exclusive to Apple Watch Series 4, which has a new electric heart rate sensor in addition to the existing optical heart rate sensor. The user fires up the software and then touches the Digital Crown for about thirty seconds, which prompts electrodes built into both the Digital Crown and the back crystal to read your heart’s electrical signals.

This in turn generates an ECG waveform. The app even indicates whether your heart rhythm shows signs of atrial fibrillation, which is a serious form of irregular heart rhythm.

The generated ECG is similar to a single-lead electrocardiogram.

The captured data is saved in the Health app on iPhone. Apple has worked with the FDA to obtain clearance so that users could send their ECG reading as a PDF to a doctor.

“It’s a momentous achievement for a wearable device that can provide critical data for doctors and peace of mind for you,” Apple claims.

Because the app is regulated, it’s only available in regions cleared for use. Initially, it’ll be limited to the US. Series 4 models sold worldwide also have the electrical heart sensor and Apple is apparently working on future expansion in Europe and elsewhere.

International users that don’t have access to the app might be able to force it to appear on their device by changing their regional settings to English (US), which also enables other features with limited availability, like Apple News, Siri and more.

watchOS 5.1.2 is currently being beta tested.